Electron guns are well known to produce electron beams and are used in several fields, including television receivers, scanning electron microscopes, defect detection instruments, VLSI testing equipment and electron beam lithography. The electron gun power supply typically used is a DC high voltage power supply (HYPS). High voltages are required to power the various electrodes, which accelerate, focus, and deflect the electron beams within an electron beam (e-beam) column which is a typical use of an electron gun. Typically, the power supplies operate at a floating potential between 10 kV and 100 kV in, for example, e-beam columns in lithography systems. In many of these applications, the electron gun is an assembly mounted on the upper portion of an electron beam column.
It is a well known deficiency that an interconnecting cable must be used to electrically connect the HVPS to the electron gun (see FIG. 1). Typically, a computer or controller (not shown) controls a module 103 which includes a DC power supply (a HVPS), which in turn supplies a high voltage, and other signals, to an electron gun 105, which is mounted at one end of an electron beam column 107. Being very sensitive to vibration, the electron gun 105 and electron beam column 107 are mounted on a vibration-isolated floating work table 113. Having large, heavy transformers and power conditioning circuits, the module typically weighs 50 to 80 pounds, and thus cannot be mounted directly on the electron gun, but is mounted on a stand-alone structure 115 in contact with the ground (hence, it is often called a rack-mounted HVPS design). A heavy high voltage cable 109 routes the power and signals from the module 103 to the electron gun 105. Vibrations on the ground or from the rack itself can transmit through the heavy, stiff cable to the electron gun and produce vibrations in the electron beam column which is not acceptable when conducting electron beam lithography.
The cable is very expensive, especially when used in conjunction with a Thermal Field Emission (TFE) electron gun, and may represent a significant portion of the cost of the entire system. The cable is expensive in large part because it is difficult to make; the insulation material must be a high-quality silicone rubber, which is free from air pockets which contribute to arcing. Moreover, it must be flexible enough to prevent vibrations, both internally and externally produced by the HVPS, from being transmitted along the cable to the vibration-sensitive electron gun. The heavy, complex mating assemblies 111 between the high voltage cable and the electron gun on one end, and between the cable and the power supply on the other end, must be nearly perfect; if they are not, electrical current will be discharged to the surrounding air (arcing).
Another disadvantage of the cable is its high capacitance. When arcing does occur from the cable, which is at a high operating voltage (for example, 50,000 V) and a high capacitance, a great deal of energy is released. This energy is often transmitted to the electron gun or the HVPS, often resulting in damage to these components.